This invention relates to a chuck unit for automatic machine tools, designed to perform both power tasks and high-speed finishing of pieces, with lubricant/coolant fluid flowing through the chuck shaft. For this purpose, the unit in accordance with the invention comprises two coaxial chucks fitted one inside the other, driven by separate motors or by the same motor.
In particular, the unit in accordance with the invention is designed in such a way that when tasks are performed with the power tool, the pull exerted by that tool on the upstream mechanical parts is only discharged onto the supporting structure of the power chuck, and no stresses are transmitted to the bearings of the second (speed) chuck.
The result is a unit which can receive different types of tool and perform different types of task, for which it has so far been most advantageous to use two separate machines.
Modern automatic machine tools designed to perform milling and contouring tasks, etc., comprise a structure to which an operating head with a number of degrees of freedom is fitted; this head comprises an end effector generally constituted by a chuck or an electric chuck, to which the tool required for each job is fitted.
The characteristics of these operating heads vary considerably, especially in chip-forming tasks, depending on whether the tasks performed are power tasks carried out with a roughing tool which rotates at a relatively low speed (approx. 2000-3000 rpm) to remove large amounts of material, and is therefore subjected to considerable stress, or finishing tasks in which the tool rotates at a much higher speed (15-20,000 rpm) to perform a finishing task, and therefore removes small amounts of material. The stresses to which the tool is subjected and the reactions it discharges onto the upstream devices require the use of chucks of different characteristics and dimensions, which necessitates the construction of different operating heads.
For this reason, when two different types of task need to be performed, separate machines are often used, partly because of the time taken to replace these heads and reset the machine. However, the need is felt for a machine which can perform both types of task, ie. power and speed tasks, with no need to replace the operating head or the end effectors.
This solution would bring considerable savings, enabling even small companies to equip themselves suitably with automatic machines of this kind.
This problem is now solved by the present invention, which relates to a chuck unit for automatic machine tools designed to perform both power and finishing tasks. The said unit comprises (i) two chucks mounted coaxially, one inside the other, (ii) means which allow a tool for roughing work and a tool for finishing work to be fitted to the said chucks, and (iii) means designed to discharge onto the structure of the assembly the pull exerted on the cone of the tool when the tool is fitted.